It is the primary purpose of this project to study some of the pertinent factors which influence cell differentiation and malignant transformation, using techniques and approaches which range from the microscopic to the molecular level. Particular emphasis is given to those systems in which murine RNA tumor viruses or their precursors may be the transforming agent. A variety of mouse model systems are used, including plasma cell tumors, mammary tumors, and neuroblastomas. Current projects include: 1) characterization of the properties of intracisternal A particles; 2) effects of interferon on the assembly of murine oncornaviruses; 3) image analysis of virus particles using a computerized scanning electron microscope system; 4) correlation of cell ultrastructure with immunoglobulin synthesis in Abelson virus-induced plasma cell tumors and lymphosarcomas. BIBLIOGRAPHIC REFERENCES: Wivel, N. A. and Yang, S. S.: Murine Neuroblastoma Clones with Varying Degrees of C-type Virus Expression. Int. J. of Cancer 18:236-242, 1976. Yang, S. S. and Wivel, N. A.: Physicochemical analysis of the Deoxyribonucleic Acid Product of Murine Intracisternal A Particle RNA-Directed DNA polymerase. Biochim et Biophys Acta 447:167-174, 1976.